The present invention relates to an exposure apparatus and a manufacturing method for a device such as a semiconductor element or a liquid crystal element, wherein a photosensitive substrate is exposed to a fine semiconductor circuit pattern such as an LSI pattern or the like. A projection exposure device is conventionally used for manufacturing an IC, an LSI, a liquid crystal element or the like using photolithography, wherein a pattern of a photo-mask or a reticle (mask) is projected onto a substrate such as a wafer, glass plate or the like coated with a photo-resist or the like through a projection optical system.
The increase of the density of the semiconductor device such as an IC, an LSI, a liquid crystal element or the like element is further accelerated. The demand for the fine process of the semiconductor wafer, therefore, increasingly requires finer pattern formation.
In response to such a demand, the projection exposure technique most influential to the fine process technique is intended to form an image of not more than 0.3 xcexcm.
However, it is difficult to form a pattern of not more than 0.15 xcexcm by en exposure device of a projection exposure type using an excimer laser which is currently dominant. The projection optical system involves a limit resulting from an unavoidable trade-off of the optical resolution and the depth of focus determined by the wavelength of the light used. The depth of focus and the resolution of the pattern by the projection exposure device are determined by Rayleigh""s equation.
R=xcexa1 (xcex/NA)xe2x80x83xe2x80x83(1)
DOF=xcexa2 (xcex/NA2)xe2x80x83xe2x80x83(2)
Here, xcex is a wavelength, NA is a numerical aperture representing the brightness of the optical system, xcexa1, xcexa2 are constants determined by the developing process property of the photosensitive substrate, and are normally 0.5-0.7. From these equations (1), (2), the increase of the resolution (reduction of the resolution R) requires the use of a short wavelength light, or a high NA. However, the depth of focus DOF of the projection optical system has to be maintained at a certain level. Therefore, it is impossible to increase the NA beyond a certain level, with the result that reduction of the wave length is the sole Solution.
However, with the reduction of the wave length, no usable glass material is available for the projection optical system. The availability of the glass material is a concern in view of the transmission factor, the durability, the refractive index uniformity, the optical strain, the machinability or the like.
Thus, the reduction of the wavelength is necessary since the equations (1), (2) are ruling in the conventional projection exposure with the result of difficulty in realizing the resolution of not more than 0.15 xcexcm.
As for an exposing type which increases the resolution, overcoming the problems, there are some proposals. In one of them, there is a method wherein multiple exposures each having a low exposure amount not enough for the resist to sense, are carried out, with different exposure patterns, so that the amount of exposure of the portion s superimposedly exposed are enough for the resist to be sensitive, by which fine patterns are formed. In such a method, the accuracy in the alignment between or among the exposure patterns is an important disassembly meter. However, such a method is not yet firmly in practice.
The alignment accuracy between the exposures in the multiplex exposure, has to be maintained high.
Accordingly, it is a principal object of the present invention to provide an apparatus and a method which are capable of manufacturing high accuracy and high density devices, and a mask therefor.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention take in conjunction with the accompanying drawings.